Inserting Hex Nuts: To assure that hex nuts are properly seated, do the following:

Insert a screw through a washer.

Insert the screw through the hole on the flat side (not the hex cavity side).

Add the hex nut on the screw and tighten the screw.

Ensure the hex nut is aligned with the hex cavity while tightening.

When the nut is fully seated, you need to remove the screw being careful not to dislodge the nut.

Inserting Nyloc Nuts: You can use the same method as hex nuts.

Inserting Square Nuts: They tend to fall out if the piece holding them is inverted. After they are inserted, check that they are properly seated by inserting a screw to engage that nut.